gh-40749: small cleanup of the file splitting_algebra.py
    
in preparation for #40213

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
    
URL: #40749
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager